Writing "game" online?

I'm an aide in a 2nd grade room. I have the kids set up with Prodigy math, Kids A-Z for reading, and spelling city, but the classroom teacher wants a writing app. She's not good with technology so I told her I would research. Does anyone know of one? I would want one that has passwords so kids can't go on other kids' accounts and screw around and make drama, and also would want the ability for us (teacher and I) to view what they have been working on. Optional want is that it has an app on iPads, but if it's just a website, that would be ok. Thx